1. Field of the Invention
The present invention relates to a process for the production of esters for use in a variety of products such as perfumes, jet engine oils, grease for use at a low temperature, heat-resistant engine oils, refrigerating machine oils, rubbers, inks and coating compositions. More specifically, it relates to a process for the production of a mixture of esters from an olefin, carbon monoxide and an alcohol, which mixture is advantageously used as an engine oil and a refrigerating machine oil.
2. Description of the Prior Art
Conventionally, an ester is produced by the reaction of dehydration in which a fatty acid and an alcohol are heated in the presence of a catalyst, as is described, e.g., in U.S. Pat. No. 5,202,044. The catalyst used for the above dehydration is selected from acid catalysts such as sulfuric acid and p-toluenesulfonic acid and organic titanate compounds such as tetrapropyl titanate.
The reaction of the above dehydration is an equilibrium reaction, and an excess of an alcohol is used. The reaction is promoted by removing formed water from the reaction system. Generally, however, the reaction rate is low, and it requires a long period of time to complete the reaction. Further, for producing an ester, for example, from a branched fatty acid such as rico-acid type, it is required to proceed with the reaction at a high temperature of at least 200.degree. C. for at least 10 hours. As a result, it is required to use a large-volume reactor of a high-quality material, and it requires an additional cost.
For avoiding the reaction which is carried out at a high temperature for a long period of time, JP-A-4-314793 and JP-A-5-1291 propose a method in which an ester is produced through an acid chloride.
In the above method of the esterification through an acid chloride, however, it is first required to produce the acid chloride from a carboxylic acid, and for this purpose, acid chlorides of inorganic acids such as phosphorus trichloride, phosphorus pentachloride or thionyl chloride are used. These acid chlorides of inorganic acids are difficult to handle, and require complicated steps.
As described above, in the conventional processes for the production of esters, the reaction rate is low and it is required to use a large-volume reactor formed of a high-quality material when they are produced by the dehydration reaction between fatty acids and alcohols. Further, in the method in which an ester is formed through an acid chloride, a complicated step is required, since acid chloride of inorganic acid is used.
Further, esters are used in various fields as described above, and esters having performances required in various fields are selected or esters having different performances are mixed. For example, in various engine oils and refrigerating machine oils, the kinematic viscosity is particularly important, and the kinematic viscosity is adjusted by changing combinations of fatty acids and alcohols or by mixing a low-viscosity ester with a high-viscosity ester. For carrying out the esterification of various combinations, it is required to purchase or synthesize various raw materials, and it is also required to carry out the reaction under conditions suitable for the raw materials. For this reason, the reaction procedures are complicated, and it is difficult to produce various products efficiently. Further, when a low-viscosity ester and a high-viscosity ester are mixed, it is difficult in many cases to satisfy the performance and physical properties required.